Added support for irregular version strings of GMP.

* jamroot: Modified regular expressions to accept irregular version strings
           of GMP.
* gmp/latest.sh: Likewise.
* gmp/jamfile: Added build script to rename the top directory of GMP source
               trees in order to fit irregular version strings to ones
               expected in sequel build procedure.
Merge pull request #82 from Cryolite/fix/gmpVersion

Added support for irregular version strings of GMP.